The present application relates to microelectronic assemblies and, in particular, to packages incorporating passive elements, especially discrete resistive and/or capacitive elements, as well as to stacked packages, and to components and methods useful in making such assemblies.
Many types of semiconductor chips contain integrated circuits which require passive elements, e.g., discrete resistive, capacitive and/or inductive devices to be mounted in close proximity to input/output pads of the chip and other pads, for purposes such as impedance matching, i.e., termination of a transmission line, DC (direct current) blocking, decoupling, or other purposes. This is especially true of integrated circuits for memory devices, and communication devices, e.g., especially high-speed serial communication interfaces and radio communication devices.
While passive elements can sometimes be incorporated within semiconductor chips, they are usually limited to very small value devices, due to the relatively large amounts of the chip device area that they tend to occupy. Larger value devices can only be provided external to the chip. Therefore, in the aforementioned memory and communication devices, many of the required passive devices must be provided off of the chip. Indeed, some chips require hundreds of such passive elements per package.
The need for external passive elements poses difficulties to the design and fabrication of a microelectronic assembly such as the chip package and higher order assemblies. A large number of passive elements is difficult to incorporate onto a circuit panel to be mounted to the package. It also becomes very difficult to route wiring traces on a circuit board between all of the required passive elements and the signal I/O of the chip. In addition, superior performance can sometimes be achieved when the passive element and the I/O pad of the chip are disposed in close proximity. Accordingly, it would be desirable to provide a way of mounting passive elements in a package which addresses these and other concerns.